The present invention relates to frontend modules for filtering transmitted and received signals in a wireless network according to operational frequency bands. More particularly, and not by way of limitation, the present invention is directed to a frontend module for Time Division Duplex (TDD) with Carrier Aggregation (CA), wherein the frontend module reuses the band selection filters for the aggregated bands and provides switched connections to antenna and transmitter/receiver according to the Uplink (UL)/Downlink (DL) configuration.
With ever-increasing demand for wireless communication and broadband services, there is an ongoing evolution of Third Generation (3G) and Fourth Generation (4G) cellular networks like High Speed Packet Access (HSPA), Evolution-Data Optimized (EV-DO), Long Term Evolution (LTE), Worldwide Interoperability for Microwave Access (WiMAX), International Mobile Telecommunications-Advanced (IMT-Advanced) (e.g., LTE Advanced), etc., to support ever-increasing performance with regard to capacity, peak bit rates and coverage. Operators deploying these networks are continuously facing the need to provide radio channel resources that can accommodate more “traffic.” In case of a mobile communication environment, such as Third Generation Partnership Project's (3GPP) LTE network, the Evolved Universal Terrestrial Radio Access (EUTRA) or Evolved Universal Terrestrial Radio Access Network (E-UTRAN) air interface for LTE may support wireless broadband data service at a rate of up to 300, Mbps in the downlink (DL) and 75 Mbps in the uplink (UL).
The LTE Release-10, (“Rel-10”) standard has recently been standardized, supporting bandwidths larger than 20, MHz. One important requirement in LTE Rel-10, is to assure backward compatibility with LTE Rel-8. This also includes spectrum compatibility, which would imply that an LTE Rel-10, carrier, wider than 20, MHz, should appear as a discrete number of LTE carriers to an LTE Rel-8, terminal. Each such carrier can be referred to as a Component Carrier (CC). In particular, for early LTE Rel-10, deployments, it can be expected that there will be a smaller number of LTE Rel-10-capable terminals compared to many LTE legacy terminals (i.e., Rel-8, terminals). Therefore, it is necessary to assure an efficient use of a wide carrier also for legacy terminals—i.e., it should be possible to implement component carriers in such a way that legacy terminals can be scheduled in all parts of the wideband LTE Rel-10, carrier. One straightforward way to obtain this is by means of Carrier Aggregation (CA). CA implies that an LTE Rel-10, terminal can receive multiple CCs, where each CC has, or at least the possibility to have, the same structure as a Rel-8, carrier.
It is understood that transmission and reception from a node (e.g., a base station) or a terminal (e.g., a mobile handset) in a cellular system, such as the LTE, can be multiplexed in the frequency domain or in the time domain (or combinations thereof). Frequency Division Duplex (FDD) implies that downlink (DL) and uplink (UL) transmissions (whether simultaneous or not) take place in different, sufficiently-separated, frequency bands. Time Division Duplex (TDD), on the other hand, implies that DL and UL transmissions take place in different, non-overlapping time slots. In TDD, the same (single) carrier frequency is possible for both UL and DL transmissions because these transmissions are separated in time domain. However, in FDD, there may be two different carrier frequencies—one for UL transmission and one for DL transmission. Thus, TDD can operate in an unpaired spectrum, whereas FDD may require a paired spectrum.
FIG. 1 illustrates an example of carrier aggregation with reference to exemplary spectrum allocations for FDD, TDD, FDD with Carrier Aggregation (FDD-CA), and TDD with Carrier Aggregation (TDD-CA). In FIG. 1, plots 10 and 11 depict exemplary UL and DL spectrum allocation, respectively, for FDD communication (without CA), and plot 12 depicts an exemplary frequency band that is common for both UL and DL for TDD communication (without CA). In FIG. 1, and also in all other figures discussed below, only two carriers (or CCs) are assumed for CA as can be seen from spectra 14-15, 17-18, and 20-21. However, it is noted here that the plots in FIG. 1 are just to provide examples of spectrum allocation in various LTE transmission schemes. As is understood, there may be more than two CCs aggregated for CA, and the teachings of the present invention (discussed below) may equally apply to any such number of carriers in a CA scheme. When CA is supported for two carriers, one carrier is on the higher band (HB) and the other carrier is on the lower band (LB)—as can be seen, for example, from the LB plots 14-15 versus HB plots 17-18 for FDD-CA (in which different frequency bands may be needed for UL and DL transmissions as mentioned earlier) and from the LB plot 20 versus the HB plot 21 for TDD-CA (in which the same LB or HB spectrum may be used for both UL and DL transmissions as mentioned earlier). In the discussion below, it is assumed for simplicity that, in the case of FDD, the uplink (UL) band is always lower than the downlink (DL) band for a CC—as can be seen from plots 14-15 and 17-18 in FIG. 1. However, again, the teachings of the present invention are not limited to any such specific placement of UL and DL frequency bands or specific bandwidth of a given carrier band.
It is observed here that modern Integrated Circuit (IC) technology helps reduce the cost of radio implementation. However, there are still many key radio components that cannot be integrated into ICs. Such limitation is seen as a bottleneck in further cost saving. In particular, the so-called “frontend module” (discussed in more detail below) placed between antenna and transmitter/receiver in a wireless communication unit becomes more costly because of its lack of integration into an IC, even when the Radio Frequency (RF) IC becomes relatively cheaper thanks to scaling down offered by Complementary Metal-Oxide Semiconductor (CMOS) technology. A frontend module typically consists of numerous filters and switches, which support the required band selection (e.g., before transmission to and after reception from an antenna) and isolation (between transmitter and receiver signals) for multimode and multiband radios.
As mentioned before, FDD allows simultaneous transmission and reception, which requires the frontend module to isolate the receiver from the transmitter, for example, against transmit leakage or receiver noise. The so-called “duplexer” plays such a role, which can be seen as a combination of two band selection filters, with one for the transmit band and the other for the receive band. Half-duplex FDD relaxes the design requirement of frontend module by prohibiting simultaneous transmission and reception on User Equipment (UE) side, thereby removing the need for a duplexer for UE. As mentioned earlier, TDD prohibits simultaneous transmission and reception (in both eNodeBs (or base stations) and UEs), and therefore it helps the cost saving of the radio hardware.
As briefly mentioned earlier, recently, cellular systems have introduced carrier aggregation (CA) that supports simultaneous transmission and reception of multiple carriers (also referred to as Component Carriers or CCs). These carriers or CCs may be either inter-band or intra-band, and also either contiguous or non-contiguous. CA poses more challenge to the design of a frontend module, because multiple aggregated carriers/CCs need to be isolated from each other in transmit and receive chains of a wireless unit. TDD with carrier aggregation (i.e., TDD-CA) may require several duplexers in both eNodeBs and UEs, especially when the UUDL subframe configuration is different among the aggregated carriers.
FIG. 2 shows a conventional frontend module 23 for FDD. The frontend module 23 consists of two band selection (or band pass) filters—filter 25 for UL (band 10) and filter 26 for DL (band 11). For ease of reference, in FIG. 2 and also in FIGS. 3-6 and 9-10, all relevant frequency band(s) (from the set of various frequency bands shown in FIG. 1) is/are shown along with the corresponding frontend module for that frequency band(s). For example, in FIG. 2, frequency bands 10-11 are shown, whereas in FIGS. 5A-5F bands 20-21 are shown, etc. However, in view of discussion of FIG. 1, no additional discussion of such frequency bands is provided with reference to FIG. 2 or any of the other figures from FIGS. 3-6 and 9-10. Also for ease of reference, the following abbreviations are used in FIG. 2 and elsewhere in the discussion herein: “BPF” refers to “Band Pass Filter”, “TX” refers to “transmitter”, “RX” refers to “receiver”, “ANT” refers to “antenna”, “o/p” refers to “output”, “i/p” refers to “input”, and “U” and “D” refer to “uplink” and “downlink”, respectively. In the context of a wireless communication unit, UL signals are considered to be “transmitted signals” whereas DL signals are considered to be “received signals.” As mentioned earlier, the frontend module 23 may be placed between an antenna 27 and a transmitter-receiver pair (including the transmitter 28 and receiver 30) in the wireless unit (not shown). Thus, the UL filter 25 in the frontend module 23 may block the leakage of the noise from the transmitter 28 into the receiver 30, while the DL filter 26 may protect the receiver 30 from the transmit signal (which may be simultaneously sent to the UL filter 25 by the transmitter 28). Note that, throughout the discussion herein, the band selection filters or BPFs are assumed to operate in a unidirectional fashion, or, at least, they are assumed to have been optimized for filtering in a single direction. For instance, each band selection filter 25, 26 in FIG. 2 has two ports 32-33 and 35-36, respectively, and the filter design is assumed to be optimized in the direction from the port with a “diamond” mark (e.g., ports 32 and 35 in FIG. 2) to the other port with an “arrow” mark (e.g., ports 33 and 36 in FIG. 2). For ease of discussion, a “diamond” marked port may be referred to as an “input port” and a port with an arrow may be referred to as an “output port.” The same convention may be valid for the transmitters and the receivers as well—i.e., transmitters with output ports (e.g., the transmitter 28 with an output port 38) and receivers with input ports (e.g., the receiver 30 with an input port 39). The antenna 27 is bi-directional in the sense that it can perform both transmissions and receptions and, hence, there may not be such uni-directional “ports” associated with the antenna 27 (or any other antenna discussed later below).
It is noted here that, unlike TDD, there is no switching needed for FDD between UL and DL signaling (because of dedicated/separate spectrum allocations for UL and DL) and, hence, the frontend module 23 is hardwired to the antenna 27, the transmitter 28, and the receiver 30. More specifically, the antenna 27 is hardwired into the input 35 of the DL filter 26 and the output 33 of the UL filter 25 as indicated by solid lines 41, 42, respectively. Similarly, the transmitter 28 is hardwired into the input 32 of the UL filter 25, while the receiver 30 is hardwired into the output 36 of the DL filter 26 as indicated by solid lines 43, 44, respectively. It is noted here that the solid lines 41-44 are for hardwiring-related illustration only; they do not represent actual hardwires. As indicated by the dotted box 23 in FIG. 2, a duplexer or frontend module for FDD is typically a 3-port device—one transmit port 32 for connection to the transmitter 28, one receive port 36 for connection to the receiver 30, and one antenna port for connection to the antenna 27. The antenna port may be considered a “combination” of ports 33 and 35 and may be collectively represented by junction point 45 indicating that the duplexer's 23 antenna side is hardwired into both the input of the DL filter and the output of the UL filter. As will be explained later in conjunction with FIGS. 5A-5F, it is possible to use this FDD duplexer (or frontend module) design to support TDD-CA.
It is pointed out here that because of detailed introduction through FIG. 2 and because of self-evident nature of input/output ports and various signaling connections in the drawings presented herein, every input port (marked with a diamond shape) or output port (marked with an arrow) and every hardwired or switching connection may not be labeled or specifically identified in every subsequent drawing to maintain clarity of figures and ease of discussion. It is understood that, if needed, such ports and connections in other figures may be easily identified like in FIG. 2.
FIGS. 3A-3C show the operations of a conventional frontend module for TDD. In case of TDD, the “frontend module” is nothing but a switch (which is not shown, but could be a simple transistor switch) connecting the antenna 48 with either the transmitter 50 or the receiver 51. The switch plays a role of isolating the receiver from the transmitter. In FIG. 3A, the switch connects the transmitter 50 to the antenna 48 to enable transmission of UL signals during the relevant subframe time. Such switched connection is illustrated by line 53 in FIG. 3A. In FIG. 3B, the switch connects the antenna 48 to the receiver 51 to enable reception of DL signals during the relevant subframe time. Such switched connection is illustrated by line 54 in FIG. 3B. FIG. 3C combines the switching individually illustrated in FIGS. 3A and 3B, and provides the overview (via dotted lines 53-54) of both switched connection possibilities of conventional frontend module for TDD. Of course, depending on the implementation choice, there may be some band selection filters in a TDD frontend module, but the specifications for such filters are usually far looser than those for conventional duplexers (e.g., FDD duplexers discussed above with reference to FIG. 2). Therefore, TDD helps the cost saving of radio implementation, since the filter, if any, is not required to satisfy a stringent filter specification.
FIGS. 4A and 4B show a conventional frontend module 56 for FDD-CA. As mentioned before, carrier aggregation with two CCs is assumed throughout the CA-related discussion herein. Therefore, the frontend module 56 for FDD-CA in FIG. 4A is shown to include two FDD duplexers 57-58. It is seen that two FDD duplexers 57-58—i.e., one duplexer for each carrier—support FDD-CA. The HB duplexer 57 consists of two band selection filters 59-60 for HB DL and HB UL and connects an HB antenna 62 to an HB transmitter 64 and an HB receiver 65. The LB duplexer 58 consists of two band selection filters 67-68 for LB DL and LB UL and connects an LB antenna 70 to an LB transmitter 72 and LB receiver 73. Thus, the FDD-CA frontend module 56 consists of four band selection filters: two filters 59-60 for HB and the other two filters 67-68 for LB. Similar to the case shown in FIG. 2, there is no switching needed for FDD-CA, and, hence, the frontend module 56 can be hardwired with corresponding antennas and transmitters/receivers as shown by solid lines (similar to those discussed with reference to FIG. 2, but not individually labeled for the sake of clarity as mentioned before) in FIG. 4A. The two UL filters 59, 68 block the noise of the corresponding transmitters 64, 72 from leaking into the corresponding receivers 65, 73; they also protect each other's signals from leaking into the other band. Likewise, the two DL filters 59, 67 protect their receivers 65, 73 from the transmit signals or each other's receive signals. The connection of the frontend module 56 with the antennas and transmitters/receivers in FIG. 4A can be seen as a simple extension of the connection shown in FIG. 2.
In FIG. 4A and other figures discussed later below, the transmitter/receiver blocks and antennas may be shown surrounded by dashed lines to indicate the components that can be optionally integrated into a single multiband component. FIG. 4B shows an example of such integration for the configuration of FIG. 4A. Thus, for example, the HB antenna 62 and the LB antenna 70 in FIG. 4A are shown to be replaced by a single multiband antenna 75 in FIG. 4B, depending on the implementation choice. Likewise, the band-specific transmitters 64, 72 in FIG. 4A and/or the band-specific receivers 65, 73 in FIG. 4A can be replaced by a multiband transmitter 77 and/or a multiband receiver 78, respectively. Except for the wideband antenna 75, wideband transmitter 77, and wideband receiver 78, all other components and hardwired connections are identical between FIGS. 4A and 4B as shown. Thus, configurations in FIGS. 4A and 4B remain functionally equivalent.
FIGS. 5A-5F illustrate how conventional FDD duplexer configurations can be used in a frontend module 80 for TDD-CA. In FIGS. 5A through 5D, different LB- and HB-based UL and DL signaling configurations (e.g., simultaneous UL transmissions on different CCs in different bands are indicated as LB-U and HB-U in case of FIG. 5A, simultaneous DL receptions on different CCs from different bands are indicated as LB-D and HB-D in case of FIG. 5B, etc.) and corresponding signaling connections (with respective transmitter/receiver) for the frontend module 80 are shown. Like FDD-CA, in the case of TDD-CA also there are multiple UUDL carriers and thus signal isolation is needed among the transmitters and the receivers. The required isolation can be achieved by using conventional FDD duplexer-type configurations 82-83 as shown in FIGS. 5A-5E. In case of FIGS. 5A-5E (and also in case of FIGS. 6A-6E discussed later), it is assumed that the frequency difference between the HB and the LB is so large that two band-specific antennas (e.g., antennas 85-86 in FIGS. 5A-5E) are needed in a mobile communication unit (not shown). It is noted here that an FDD duplexer (e.g., duplexer 23 in FIG. 2, or duplexers 57-58 in FIGS. 4A-4B) always has its two band pass filters hardwired on its antenna side. In case of FIGS. 5A-5E, the HB duplexer 82 consists of two identical band selection filters 88-89 for the HB and the LB duplexer 83 also consists of two identical band selection filters 90-91 for the LB. These BPFs 88-91 are shown hardwired (by using exemplary lines 93-96, which are labeled in FIGS. 5A and 5E only for the sake of clarity and to avoid undue repetition in other figures) to respective HB and LB antennas 85-86. It is noted here that, strictly speaking, these duplexer-type configurations 82-83 may be considered different from the conventional FDD duplexers in the sense that a conventional FDD duplexer consists of two different band selection filters (for two different bands—like bands 10-11 in FIG. 2, or HB bands 17-18 in FIGS. 4A-4B, etc.) isolating the receiver from the transmitter. On the other hand, each pair of BPFs 88-89 or 90-91 in FIGS. 5A-5E is for a single band—Either band HB-U/D 21 or band LB-U/D 20. In any event, the conventional FDD duplexers (with two different band selection filters) can be used, for example, when the HB and the LB are close enough to enable usage of a wideband antenna, as shown in FIG. 5F, which is discussed later below.
In FIGS. 5A-5D, two band-specific transmitters 98-99 and two band-specific receivers 102-103 are shown in different switched connections with relevant BPFs in the frontend module 80. Thus, on the transmitter/receiver side, the frontend module 80 may need appropriate switches (not shown) for the transmitters 98-99 and the receivers 102-103, according to the UL/DL configuration of the corresponding LTE subframe. Through different lines (e.g., lines 105-108) connecting appropriate BPFs, in the frontend module 80 with corresponding transmitter(s) and/or receiver(s), FIGS. 5A-5D illustrate examples of how to set the switches for different UL/DL configurations. It is noted here that lines 105 through 108 in FIGS. 5A-5D illustrate switched connections only—i.e., the lines are used merely to illustrate different signal switching arrangements in FIGS. 5A-5D and they do not depict any hardwired connections. Similar such lines are shown in FIGS. 6A-6D to illustrate different switched connections (this time between the antennas and the frontend module) as discussed later below. All individual switching possibilities shown in FIGS. 5A-5D are depicted combined in FIG. 5E, in which solid lines 93-96 are used to indicate hardwired connections (as between antennas 85-86 and the frontend module 80) and dashed lines 105-108 are used for various switched connections already shown in FIGS. 5A-5D.
As mentioned before, where the frequency difference between the HB and the LB is small enough, a designer may use wideband antennas and/or wideband transmitters/receivers instead of individual band-specific components for these entities. FIG. 5F exemplifies the use of a wideband antenna 110 (without any wideband transmitter or receiver) in conjunction with a frontend module 112. In this case, the frontend module 112 consists of two conventional FDD duplexers 113-114 that can support TDD-CA for all possible UUDL configurations. Each duplexer 113-114 includes a corresponding pair of HB and LB band-specific BPFs 116-117 and 119-120, respectively. Thus, contrary to duplexer-type configurations in FIGS. 5A-5F, each duplexer 113-114 in FIG. 5F has two truly different band selection filters like a conventional FDD duplexer as noted earlier. As in case of the frontend module 80 in FIGS. 5A-5E, the frontend module 112 has switches (not shown) on the transmitter/receiver side (as indicated by dashed lines 122-125 for such switched connections) and hardwired connections on the antenna side (as indicated by solid lines 127-130). The band-specific transmitters 98-99 and receivers 102-103 in FIG. 5F may be the same as those shown in FIGS. 5A-5E.
FIGS. 6A-6E depict another frontend module 133 for TDD-CA in which switches are introduced on the antenna side (as represented by lines 135-138 in FIGS. 6A-6D connecting appropriate BPFs with corresponding antennas 140-141) and the transmitter/receiver side is instead hardwired (as indicated by exemplary lines 143-146 connected to appropriate transmitters 148-149 and receivers 150-151 as shown). It is noted here that lines 143-146 are labeled in FIGS. 6A and 6E only for the sake of clarity and to avoid undue repetition in other figures. As before, relevant TDD-CA frequency bands 20-21 are shown at the top in each of the FIGS. 6A-6E for ease of reference. As mentioned before, it is reiterated here that lines 135 through 138 in FIGS. 6A-6D illustrate switched connections only—i.e., the lines are used merely to illustrate different signal switching arrangements in FIGS. 6A-6D and they do not depict any hardwired connections. All individual switching possibilities shown in FIGS. 6A-6D are depicted combined in FIG. 6E, in which solid lines 143-146 are used to indicate hardwired connections (as between the transmitter/receiver side and the frontend module 133) and dashed lines 135-138 are used for various switched connections already shown in FIGS. 6A-6D. As also mentioned earlier, the transmitter/receiver blocks and antennas are shown in FIGS. 6A-6E surrounded by dashed lines to indicate that these components can be optionally integrated into a single multiband (or wideband) component (e.g., when the spacing between the HB and LB is close enough) as shown, for example, in FIGS. 4B and 5F.
Similar to the frontend modules shown in FIGS. 5A-5F, the frontend module 133 in FIGS. 6A-6E also includes two duplexer-type filter units 153-154, each such filter unit includes two identical band selection filters for the corresponding band—one filter for the transmitter of the band and the other (identical) filter for the receiver of the band. For example, the filter unit 153 in FIGS. 6A-6E includes the BPF 156 for the receiver 150 of the HB band and the BPF 157 for the transmitter 148 of the HB band. Similarly, the filter unit 154 includes the BPF 159 for the receiver 151 of the LB band and the BPF 160 for the transmitter 149 of the LB band. However, the frontend module 133 in FIGS. 6A-6E may be considered different from the FDD duplexers shown in FIGS. 2, 4 and 5F in the sense that its BPFs are not hardwired on its antenna side, but are rather hardwired on its transmitter/receiver side as shown. It is observed here that the configurations in FIGS. 5 and 6 may be used interchangeably when switching for TDD-CA is desired.